Quantum key distribution (QKD) technology is a technique for safely sharing keys for encrypted data communication, between a transmitting node (Alice) that continuously transmits single photons and a receiving node (Bob) that receives the single photons, which are connected to each other by an optical fiber. Note that to share a key an exchange of control data through a classical channel which is called key distillation is performed between the transmitting node and the receiving node. The key as used herein is shared information to be shared between the transmitting node and the receiving node, and is a series of random numbers made up of digital data. The transmitting node (Alice) and the receiving node (Bob) are collectively referred to as nodes. It is guaranteed based on the principles of quantum mechanics that the keys shared here are not eavesdropped on.
As a protocol for system control of a quantum key distribution system, Q3P (Quantum Point to Point Protocol) is known. A LOAD subprotocol of Q3P is a protocol that stores a key generated and stored by quantum key distribution in a single storage area called a “Common Store” and determines information as to whether the key is used as an encryption key or a decryption key, between the nodes, as necessary.
However, conventional art has problems such as an increase in processing load and wasted key consumption. For example, every time a key is generated, a process such as the LOAD subprotocol needs to be performed, complicating the system configuration. In addition, the time for a key to be finally able to be used increases. In addition, extra keys are consumed to safely execute the protocol.